Loop heat pipe

ABSTRACT

A loop heat pipe includes an evaporator, a condenser, and a vapor line and a liquid line each connecting the evaporator with the condenser to form a closed loop. A predetermined quantity of bi-phase working medium is contained in the closed loop. A separator connects the liquid line. A cross section of the separator is larger than a cross section of the liquid line. The separator separates the liquid state working medium from the vapor state working medium when the working medium flows therethrough.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 from China Patent Application No. 201010258764.2, filed on Aug. 20, 2010, in the China Intellectual Property Office, the contents of which are hereby incorporated by reference.

BACKGROUND

1. Technical Field

The disclosure generally relates to heat transfer apparatuses, and particularly to a loop heat pipe with a high heat transfer efficiency.

2. Description of Related Art

Loop heat pipes are widely used for heat dissipation purposes because of their excellent heat transfer efficiency. A commonly used loop heat pipe includes an evaporator thermally attached to a heat-generating electronic component, a condenser, and a vapor line and a liquid line respectively interconnected between the evaporator and the condenser. A predetermined quantity of bi-phase working medium is contained in the closed loop. The working medium conveys heat from the evaporator to the condenser. A wick structure, lining an inner surface of the evaporator, draws the working medium back to the evaporator after it condenses at the condenser.

However, in the operation of the loop heat pipe, the vapor cannot be condensed fully to a liquid state working medium at the condenser. Instead, the condensate adjacent to the condenser is a mixture of a vapor state working medium and a liquid state working medium. The vapor state working medium entering the liquid line will obstruct the liquid state working medium flowing back to the evaporator. Thus, the liquid state working medium may not move towards the evaporator in a timely manner, and the evaporator may be prone to dry out.

What is needed, therefore, is a means which can overcome the described limitations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a loop heat pipe according to a first embodiment of the present disclosure.

FIG. 2 is a bottom view of the loop heat pipe of FIG. 1.

FIG. 3 is an isometric view of a loop heat pipe according to a second embodiment of the present disclosure.

DETAILED DESCRIPTION

Reference will now be made to the figures to describe the present loop heat pipe in detail.

Referring to FIGS. 1 and 2, a loop heat pipe 10 according to a first embodiment of the present disclosure includes an evaporator 11, a condenser 12, a separator 15, and a vapor line 13 and a liquid line 14 connecting the evaporator 11, the condenser 12, and the separator 15 to form a closed loop. The separator 15 is part of the liquid line 14. A predetermined quantity of bi-phase working medium (not shown) is filled in the closed loop. The working medium is a liquid, which has a low boiling point such as water, methanol, or alcohol. Thus, the working medium can easily evaporate to vapor when it absorbs the heat transferred to the evaporator 11 and condenses to liquid when heat is transferred to the atmosphere at the condenser 12.

The evaporator 11 can be rectangular and have a flat shape, and include a liquid inlet 110 connected to the liquid line 14 and a vapor outlet 112 connected to the vapor line 13. A wick structure (not shown) consists of a porous structure, such as a screen mesh, fiber inserted into the evaporator 11 and held against an inner surface of the evaporator 11, or sintered powder combined to the inner surface of the evaporator 11 using a sintering process. The evaporator 11 thermally connects a heat-generating electronic component to absorb heat generated therefrom.

Each of the condenser 12, the vapor line 13, and the liquid line 14 is an elongated hollow tube. The condenser 12 can be parallel to the evaporator 11, and includes a vapor inlet 121 connected to the vapor line 13, and a liquid outlet 123 connected to the liquid line 14. A heat dissipation component (not shown) thermally contacts an outer surface of the condenser 12 to dissipate heat to the atmosphere. The heat dissipation component can be a fin-type heat sink. Although not shown, the heat dissipation component can include fins for increasing the heat dissipation efficiency thereof.

The vapor line 13 and the liquid line 14 can be parallel to each other. The diameter of the vapor line 13 is substantially equal to that of the liquid line 14. Alternatively, the diameter of the vapor line 13 and the diameter of the liquid line 14 can vary, only to ensure that the diameter of the liquid inlet 110 is no larger than the diameter of the liquid outlet 123.

The separator 15 is located at a middle portion of the liquid line 14. The separator 15 includes an elongated hollow cylindrical main body 150, and a tapered entrance 151 and a reverse tapered exit 153 respectively located at two opposite ends of the main body 150. The entrance 151 is located adjacent to the liquid outlet 123 of the condenser 12. The exit 153 is located adjacent to the liquid inlet 110 of the evaporator 11. The separator 15 separates the liquid line 14 into a first portion 141 connected between the liquid outlet 123 and the entrance 151, and a second portion 142 connected between the exit 153 and the liquid inlet 110. The entrance 151 can have a trapezoid cross-section, with a diameter gradually increasing from the first portion 141 of the liquid line 14 towards the main body 150. A diameter of the main body 150 of the separator 15 is larger than that of the liquid line 14. Thus, a capacitance of the separator 15 is larger than that of a portion of the liquid line 14, which has substantially the same length as the separator 15. In this embodiment, the diameter of the main body 150 is about twice as large as the liquid line 14. The exit 153 has a similar cross-section as the entrance 151 but only differs in orientation, with the diameter gradually decreasing from the main body 153 towards the second portion 142 of the liquid line 14.

During operation of the loop heat pipe 10, the working medium in the evaporator 11 absorbs heat from the heat-generating electronic component and vaporizes to a vapor state working medium. The vapor pressure of the vapor state working medium expels the vapor state working medium, carrying heat with it, to flow through the vapor line 13 by the vapor outlet 112 of the evaporator 11. Then, the vapor state working medium enters into the condenser 12 by the vapor inlet 121. At the condenser 12, the vapor state working medium dissipates the heat to ambient environment and condenses to a condensed working medium. The condensed working medium flowing out of the liquid outlet 123 of the condenser 12 is then propelled through the first portion 141 of the liquid line 14, the separator 15, and the second portion 142 of the liquid line 14 in that order, and moves into the evaporator 11 by the liquid inlet 110 thereof. The condensed working medium at the evaporator 10 then evaporates into vapor again to start another heat transfer cycle.

In each heat transfer cycle described above, the vapor state working medium may not be thoroughly condensed to a liquid state working medium at the condenser 12. That is, during each heat transfer cycle, some of the vapor state working medium is not condensed to a liquid state working medium at the condenser 12, resulting in the condensed working medium flowing out of the liquid outlet 123 of the condenser 12 and forming a mixture of a liquid state working medium and a vapor state working medium. Due to the presence of the separator 15, when the condensed working medium flows from the condenser 12 towards the evaporator 11 by the liquid line 14, the separator 15 separates the liquid state working medium from the vapor state working medium flowing therethrough and then supplies the liquid state working medium to the evaporator 11 continuously.

More specifically, when the condensed working medium flows through the separator 15, the liquid state working medium contained in the condensed working medium directly drips down from a centre of the entrance 151 towards the exit 153, while the vapor state working medium circumfuses to accumulate in the interior of the main body 150. Further, the vapor state working medium contained in the interior of the separator 15 dissipates the heat to the ambient environment at the separator 15 and condenses to a liquid state working medium to flow to the evaporator 11 by the exit 153. Thus, the separator 15 can separate the liquid state working medium from the vapor state working medium when the working medium flows therethrough, to allow the liquid state working medium to flow smoothly to the evaporator 11 without obstruction of the vapor state working medium. The diameter of the exit 153 gradually decreases from the main body 150 towards the second portion 142 of the liquid inlet 14. This connects the liquid inlet 110 of the evaporator 11, such that the speed of the liquid state working medium flowing out of the separator 15 towards the liquid inlet 110 of the evaporator 11, is properly controlled.

FIG. 3 shows a loop heat pipe 20 according to a second embodiment. The loop heat pipe 20 differs from the loop heat pipe 10 of the first embodiment only in the shape of the separator 25 thereof. The separator 25 includes a tapered main body 251 connected to the first portion 141 of the liquid line 14 and a reverse tapered exit 252 connected to the second portion 142 of the liquid line 14. The diameter of the main body 251 gradually increases from the first portion 141 of the liquid line 14 towards the exit 252. The largest diameter of the main body 251 is much larger than the diameter of the liquid line 14, which makes a capacitance of the separator 25 larger than that of a portion of the liquid line 14, which has the same length as the separator 25. In this embodiment, the largest diameter of the main body 251 is about three times as large as the liquid line 14. The exit 252 has a diameter gradually decreasing from the entrance towards the second portion 142 of the liquid line 14. In this embodiment, the separator 25 can separate the liquid state working medium from the vapor state working medium in the same manner of the loop heat pipe 10.

It is to be understood, however, that even though numerous characteristics and advantages of the embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

What is claimed is:
 1. A loop heat pipe comprising: an evaporator; a condenser; a vapor line and a liquid line each connecting the evaporator with the condenser to form a closed loop; a predetermined quantity of bi-phase working medium contained in the closed loop; and a separator connected to the liquid line, wherein a cross section of the separator is larger than a cross section of the liquid line, and the separator is configured for separating a liquid state working medium from a vapor state working medium when the working medium flows therethrough.
 2. The loop heat pipe of claim 1, wherein a capacitance of the separator is larger than that of a portion of the liquid line which has substantially the same length as the separator.
 3. The loop heat pipe of claim 1, wherein the separator comprises a hollow cylindrical main body, wherein an entrance and an exit are located at two opposite ends of the main body, and a diameter of the main body is larger than that of the liquid line.
 4. The loop heat pipe of claim 3, wherein the entrance has a tapered shape with a diameter gradually increasing from an end adjacent to the condenser towards the main body.
 5. The loop heat pipe of claim 4, wherein the exit has a reverse tapered shape with a diameter gradually decreasing from the main body towards the evaporator.
 6. The loop heat pipe of claim 3, wherein the diameter of the main body is about twice as large as the liquid line.
 7. The loop heat pipe of claim 3, wherein the evaporator comprises a liquid inlet connected to a first end of the liquid line and a vapor outlet connected to a first end of the vapor line, the condenser comprises a vapor inlet connected to a second end of the vapor line and a liquid outlet connected to a second end of the liquid line, and the entrance and the exit are located adjacent to the liquid outlet of the condenser and the liquid inlet of the evaporator, respectively.
 8. The loop heat pipe of claim 7, wherein a diameter of the liquid inlet is no larger than that of the liquid outlet.
 9. The loop heat pipe of claim 7, wherein the separator separates the liquid line to a first portion connected between the liquid outlet and the entrance and a second portion connected between the exit and the liquid inlet.
 10. The loop heat pipe of claim 1, wherein the separator comprises a tapered main body and an exit located adjacent to the evaporator, a diameter of the main body increasing from one end adjacent to the condenser towards the exit.
 11. The loop heat pipe of claim 10, wherein a largest diameter of the main body is about three times as large as the liquid line.
 12. A loop heat pipe comprising: an evaporator configured for thermally connecting with a heat generating electronic component and comprising a liquid inlet and a vapor outlet at two opposite sides thereof; a condenser configured for thermally connecting with a heat dissipating component and comprising a vapor inlet and a liquid outlet at two opposite ends thereof; a separator having a cross section larger than that that of the liquid line; a vapor line connecting the vapor outlet with the vapor inlet; a liquid line comprising a first portion connecting the liquid outlet with the separator and a second portion connecting the separator with the liquid inlet; and a predetermined quantity of bi-phase working medium contained in the loop heat pipe, wherein the separator separates a liquid state working medium from a vapor state working medium when the working medium flows therethrough.
 13. The loop heat pipe of claim 12, wherein the separator comprises a hollow cylindrical main body, wherein an entrance and an exit are located at two opposite ends of the main body, the entrance and exit are located adjacent to the liquid outlet of the condenser and the liquid inlet of the evaporator, respectively, and a diameter of the main body is larger than that of the liquid line.
 14. The loop heat pipe of claim 13, wherein the entrance has a tapered shape with a diameter gradually increasing from the liquid outlet towards the main body.
 15. The loop heat pipe of claim 14, wherein the exit has a reverse tapered shape with a diameter gradually decreasing from the main body towards the liquid inlet.
 16. The loop heat pipe of claim 12, wherein the separator comprises a tapered main body and an exit located adjacent to the liquid inlet, and a diameter of the main body increases from the liquid outlet towards the exit. 